Authenticatable image with an embedded image having a discernible physical characteristic with improved security feature

ABSTRACT

A method is disclosed for printing an authenticatable image having an embedded image into a receiver having a discernible physical characteristic, such that the printed image can be used to authenticate the receiver includes scanning the receiver to produce information related to the discernible physical characteristic of the receiver, and providing a carrier which includes information related to the scanned receiver discernible physical characteristic. The method also includes combining the carrier with an input image to form the authenticatable image having the embedded image, and printing the authenticatable image having the embedded image onto the receiver.

FIELD OF THE INVENTION

The invention relates generally to the field of image processing, and inparticular to providing a secure document such as a passport, eventticket, currency, or a postal stamp, coupon or envelope.

BACKGROUND OF THE INVENTION

In U.S. patent application, Ser. No. 09/613,989, a method is disclosedthat enables the use of paper or textured media to be authenticatedbased upon an embedded signal derived from the physical texturalattributes of the media. A carrier is formed by scanning a region ormultiple regions of the media and is convolved with a message to form anauthenticable signal. After scanning, the carrier is subdivided andrearranged in ways that prevents a person from “discovering” thecarrier.

Although this method is satisfactory, it includes drawbacks. One suchdrawback is that it adversely affects the robustness of thedata-embedding algorithm. When the receiver having the carrier is beingverified as authentic, the carrier regions must be rescanned. Anyscanning errors introduced, for example, in scanning angle, in scanningstarting point, or in scanning scale are compounded proportionately tothe number of subdivisions, mirrors or other manipulations applied toimprove security. These errors affect the algorithms robustness orequivalently the data capacity of the algorithm.

Consequently, a need exists for a means to either completely overcomethe errors introduced by the rescanning process or to minimize theireffect while improving overall security of the processes.

SUMMARY OF THE INVENTION

The present invention is directed to overcoming one or more of theproblems set forth above. Briefly summarized, according to one aspect ofthe present invention, the invention resides in a method for creating anauthentic image on a receiver, the method comprising the steps of: (a)providing a first carrier formed from information related to a physicalcharacteristic of the receiver; (b) providing a second carrier that israndomly generated; (c) combining the first and second carrier such thatthe first carrier cannot be derived without the second carrier forforming a combined carrier; (d) combining the combined carrier withpredetermined content for forming the authentic image having thepredetermined content; and (e) including the authentic image having thepredetermined content on the receiver.

These and other aspects, objects, features, and advantages of thepresent invention will be more clearly understood and appreciated from areview of the following detailed description of the preferredembodiments and appended claims, and by reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a binary message image and an iconic message image asan edge map depicting a Kodak trademark;

FIG. 2 is a graph depicting the Fourier amplitude vs. the spatialfrequency of an optimally designed carrier,

FIG. 3 illustrates a receiver containing a carrier scan region picturethat has been embedded with information;

FIG. 4 illustrates a sequence of steps for converting a message into aformat appropriate for embedding into an image;

FIG. 5 is a depicts a block diagram for the process of forming a securecarrier from a scan;

FIG. 6 is a diagram illustrating convolving a message with two carriersto form a secure dispersed mesage;

FIG. 7 is a diagram illustrating correlating the embedded image with thetwo carriers for extracting the message;

FIG. 8 depicts the process, in block diagram form, of decrypting theextracting message for discerning the message.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, authenticable means capable of verifying or capable orproving authenticity.

The invention utilizes aspects of data embedding. The science of dataembedding is also referred to as data hiding, information hiding,watermarking and steganography. A preferred basic data embeddingtechnique is disclosed in Honsinger, et al., U.S. Pat. No. 6,044,156. Areview of this technique and associated embellishments to the techniqueis briefly discussed hereinbelow. An original image is represented asthe two-dimensional array, I(x,y), the embedded image, I′(x,y), and acarrier is defined as C(x,y). A message that is embedded, M(x,y), in itsmost general form, is an image. The message can represent an icon, forexample, a trademark, or may represent the bits in a binary message. Inthe latter case the on and off states of the bits are represented asplus and minus ones, or positive and negative delta functions (spikes)which are placed in predefined and unique locations across the messageimage. Reffering to FIG. 1, an example of a binary message image 2 andan iconic message image 4 is shown. Examples of iconic data types aretrademarks, corporate logos or other arbitrary images. Performancegenerally decreases as the message energy increases so edge maps of theicons are used. Examples of binary data types are 32 bit representationsof URL's, and copyright ID codes, or authentication information.

With these definitions, the preferred embedding equation is:I′(x,y)=α(M(x,y)*C(x,y))+I(x,y)  (1)where the symbol, *, represents circular convolution and α is anarbitrary constant chosen to make the embedded energy simultaneouslyinvisible and robust to common processing. From Fourier theory, spatialconvolution in the frequency domain is the same as adding phase whilemultiplying magnitudes. Therefore, the effects of combining the messagewith a carrier, such as by the described convolution technique,distributes the message energy in accordance with the phase of thecarrier and to modulate the amplitude spectrum of the message with theamplitude spectrum of the carrier. If the message were a single deltafunction and the carrier of random phase and of uniform Fouriermagnitude, the effect of convolving with the carrier would be todistribute the delta function over space. Similarly, the effect ofconvolving a message with a random phase carrier is to spatiallydisperse the message energy.

The preferred extraction process is to correlate with the same carrierused to embed the image:I′(x,y){circle around (x)}C(x,y)=α(M(x,y)*C(x,y)){circle around(x)}C(x,y) +I(x,y){circle around (x)}C(x,y),  (2)where the symbol, {circle around (x)}, represents circular correlation.Correlation is similar to convolution in that Fourier magnitudes alsomultiply. In correlation, however, phase subtracts. Therefore, the phaseof the carrier subtracts on correlation of the embedded image with thecarrier leaving the message. Indeed, assuming that the carrier isdesigned to have uniform Fourier amplitude, then, and the process ofcorrelation of the carrier on the embedded image Eq. 2, can be reducedto:I′(x,y){circle around (x)}C(x,y)=αM(x,y)+noise  (3)That is, the process of correlation of the embedded image with thecarrier reproduces the message image plus noise due to the crosscorrelation of the image with the carrier.

Tiling the dispersed message on the original image improves therobustness of the algorithm. For this invention, preferably, a single256×256 dispersed message is tiled over the entire image. Uponextraction, each 256×256 region is aligned and summed to produce thefinal message. As disclosed in U.S. Pat. No. 6,567,532, issued on May20, 2003, for imaging applications with severe quality loss, such assmall images printed using ink-jet printers on paper, a weighting factorthat depends on the estimated signal to noise ratio can be calculatedand applied to each extracted message element before summation.

The extracted message is denoted as M′(x,y), the equation for extractingthe message (Eq. 2 and Eq. 3) can be rewritten as:M′(x,y)=αM(x,y)*(C(x,y){circle around (x)}C(x,y))+noise  (4)The above equation suggests that the resolution of the extracted messageis fundamentally limited by the autocorrelation function of the carrier,C(x,y){circle around (x)}C(x,y). Any broadening of C(x,y){circle around(x)}C(x,y) from a delta function will blur the extracted message whencompared to the original message. Another way to view the effect of thecarrier on the extracted message is to consider C(x,y){circle around(x)}C(x,y) as a point spread function, since convolution of the originalmessage with C(x,y){circle around (x)}C(x,y) largely determines theextracted message.

The design of the carrier should consider both the visual detectabilityof the embedded signal and the expected signal quality at the extractionstep. There is clearly a design tradeoff between achieving optimumextracted signal quality and embedded signal invisibility.

A carrier designed for optimal extracted signal quality will possessincreasing amplitude with increasing spatial frequency. This may bederived from the well-known characteristic of typical images that theFourier amplitude spectrum falls as the inverse of spatial frequency. Atlow spatial frequencies, where typical images have their highest energyand influence on the extracted image, the present invention carrier usesthis result. In particular, the mean or DC frequency amplitude of ourcarrier is always zero. As spatial frequency is increased, the carrieramplitude envelope smoothly increases with increasing spatial frequencyuntil about 1/16 to ⅕ Nyquist.

For frequencies greater than this, the carrier envelope is derived froma Contrast Sensitivity Function (CSF). A graph representing aone-dimensional slice of the Fourier amplitude of such a carrier isdepicted in FIG. 2. Use of the CSF in an image embedding application isdescribed in greater detail in Daly, U.S. Pat. No. 5,905,819.

The CSF provides a measure of the sensitivity of the average observer tochanges in contrast at a given spatial frequency. The reciprocal of theCSF can be used to prescribe the amount of amplitude needed for theembedded signal to be detectable by an average viewer. Many modem CSFmodels facilitate for observer viewing distance, background noise,receiver dot density, color component wavelength and other factors.

Use of these CSF parameters can be an advantage when optimizing anembedding algorithm for a specific application. One particularly usefulway of sizing the embedding algorithm for a specific system is to definethe quality of the embedded signal in terms of the viewing distance atwhich the embedded signal can be visually detected. Once this isdefined, an optimized carrier can be immediately derived and tested.

For a binary message, the impact of this carrier envelope is to producea very small sidelobe around each delta function. It may be argued thatthe sidelobes limit the bandwidth of the algorithm. However, it has beenfound that the destructive processes of compression, error diffusion,printing and scanning have a far greater influence on the bandwidth ofthe algorithm. In a binary message, these destructive processes are thelimiting factor of the bit density and can be thought of as defining theminimum separation distance between the delta functions. So long as thesidelobes are confined within half of the minimum bit separationdistance, sidelobe interference may be considered minimal.

Correcting for rotation, scaling and skew is a fundamental element ofall robust data embedding techniques. In Honsinger, et.al, U.S. Pat. No.5,835,639, Method for detecting rotation and magnification in images, apreferred method of correction of rotation and scale is provided. Thecorrection technique relies on autocorrelation the embedded image. Forexample, upon autocorrelation of an embedded image that has not beenrotated or scaled, one would expect to see correlation peaks spacedhorizontally and vertically at intervals of 256 pixels and 256 lines. Atthe zero offset correlation point, there is a very high peak due to theimage correlating with itself.

Now, if the embedded image is scaled, the peaks must scaleproportionately. Similarly, if the embedded image is rotated, the peaksmust rotate by the same amount. Therefore, the rotation and scale of animage can be deduced by locating the autocorrelation peaks. Detection ofthe actual rotation angle θ is limited to angles in the range (−45°,+45°]. However, the actual rotation angle will be a member of the setθ_(actual)=θ_(calculated)±n90°, where n is an integer. Because of thepossibility that the image has been flipped or rotated in increments of90 degrees during the message extraction process, this ambiguity is nota fundamental limitation. It can be shown that this method can correctfor a general affine transform since an affine transform preservesrelative shapes. That is, a shape that is repeated twice will stillappear twice, and the new shapes will still be identical providing agood autocorrelation for realistic applications of data embedding.

The effect of the autocorrelation properties of the original image canbe significant. Without ancillary processing, high amplitude lowfrequency interference in the autocorrelation image can make the processof detecting peaks difficult. To minimize this problem, localized firstorder and second order moment normalization on the embedded image beforethe autocorrelation. This process consists of replacing each pixel inthe image with a new pixel value, v_(new): $\begin{matrix}{v_{new} = {\frac{\sigma_{desired}}{\sigma_{old}}\left( {v_{old} - m_{old}} \right)}} & (5)\end{matrix}$where v_(old), is the original pixel value, m_(old), is the local meanof the image, σ_(desired) is the desired standard deviation, which isgenerally set to the expected embedded signal standard deviation andσ_(old) is the local standard deviation. Because this operation is overa small area, typically over a (3×3) or (5×5) region, its effect inremoving the high amplitude, low frequency coherent noise is quitesubstantial. For the limiting case when σ_(old)→0, v_(new) is equated toa value taken from a random noise generator having a standard deviationσ_(desired).

The next piece of ancillary processing performed is to shape theautocorrelation peaks. This is done during the FFT operation used in theautocorrelation processing. A function that increases linearly withspatial frequency in the Fourier magnitude domain is quite satisfactory.This function is consistent with a Wiener filter designed to maximizethe semblance of the correlation peaks to delta functions under theassumption that the image Fourier amplitude spectrum exhibits anasymptotic “1/(spatial frequency)” falloff. Following these processingsteps produces peaks that need little further processing.

Importantly, because autocorrelating the embedded image requires noextra calibration signal, it does not tax the information capacity ofthe embedding system. In addition, this technique can be applied to anyembedding technique with redundant embedded signals and may implementedon a local level to confront low order geometric warps.

The ability to recover from cropping is an essential component of a dataembedding algorithm. As disclosed in U.S. Pat. No. 6,678,390, issued onJan. 13, 2004, if one were to extract from an arbitrarily located256×256 region of an embedded image, the extracted message wouldprobably appear to be circularly shifted due to the unlikely chance thatthe extraction occurred along the original message boundary.

Indeed, if the origin of the 256×256 extracted region was a distance,(Δx,Δy), from its nearest “original” origin, then the extracted message,M′(x,y) can be written as:M′(x,y)=M(x,y)*δ(x−Δx,y−Δy)  (6)where it has been assumed that the convolution is circular, that thecarrier autocorrelated to a delta function and that the imagecontributes no noise.

On the surface, this circular shift ambiguity is a severe limitation ondata capacity because it imposes the constraint that the messagestructure must be invariant to cyclic shifts. However, the presentinvention provides a way around this by placing the bits in the messagein a special manner. First, there is required the use of a “messagetemplate,” that is, a prescription of where to place the bits in amessage image. The message template is derived by placing positive deltafunctions on a blank 256×256 image such that each delta function islocated a minimum distance away from all others and such that theautocorrelation of the message template yields as close as possible, adelta function. That is, the bits are placed such that the messagetemplate autocorrelation sidelobes are of minimal amplitude.

Now, correlation of the extracted region with a zero mean carrierguarantees that the extracted circularly shifted message M′(x,y) is alsozero mean. If the message template is called, T(x,y), then the absolutevalue of the the extracted template must be practically equivalent to acircularly shifted message template. That is,|M′(x,y)|=T(x,y)*δ(x−Δx,y−Δy)  (7)This implies, due to the autocorrelation property of the messagetemplate, that the shift from the origin of the message can be derivedby correlating |M′(x,y)| with T(x,y), since: |M′(x,y)|{circle around (x)}T(x,y)=δ(x−Δx,y−Δy)  (8)Therefore, the result of the correlation will be a 256×256 image, whosehighest peak will be located at the desired shift distance, (Δx,Δy).This peak location can be used to correctly orient the interpretation ofthe embedded bits.

There are many applications of this invention to media. A paycheck, awill, a product label, or any media that it is wished to prove that itis an original. For the sake of specificity, we shall choose an envelopewith a stamp as a preferred embodiment. Here the media to be scanned toform a carrier is paper, however, it is understood that virtually anymedia will suffice as a receiver so long as it has a discerniblephysical characteristic which is subject to a reasonably high resolutionscan for producing a carrier.

In accordance with the present invention, a self authenticating mediausing a public fiber carrier and an auxiliary private carrier will nowbe described in more detail. FIG. 3 shows a medium, such as a medium 10,in this case paper, containing a scan area 12, and a picture used tohide the secure embedded image 14. FIG. 4 is a block diagram showing thesteps needed to form the message image needed to practice the inventionusing the technique outlined above. The message, shown in block 16,should contain information such as postage. If the message onlycontained postage, for example 33 cents, and if the maximum postageallowed for the size of the envelope was $2.56, then eight bits (2⁸=256)of information would be needed to convey all postage amounts. However,performance is not substantially degraded when using 32 or 64 bits, whencompared to 8 bits, providing a much greater number level ofpossibilities. Once the message has been expressed in its binary form,it is possible to encrypt, as shown in block 18, by using any desiredencryption algorithm. One encryption technique is a public/private keytechnique. Using a public/private key technique enables only the messagegenerator to know how to encrypt the message. The entity performing thevalidation or authentication can only decrypt the message with its ownkey. Public/private key encryption is well known to anyone conversant inencryption technologies. In the case of a postage stamp, a private keyencryption system would suffice given that the post office would controlboth the encryption and decryption process. However, in the case of acurrency, wherein a government authorizes many different vendors tobuild authenticating ATM (automated teller machines) a public/privatescheme would make more sense. This is because by allowing the multiplevendors of the ATM machines the same key used to generate the message,the government would increase the chances that a vendor would use thekey to generate counterfeit currency, After the encryption, the bitsshown in block 20 are placed on a message template 22 according to knownbit placement rule. As a preferred embodiment, assuming one takes thefirst bit and place it on the message template in the topmost andleftmost possible position. If the first bit is a 1, the value 1 isdisposed in a first position. If the bit is a zero, the value a −1 inthe first position. The next bit from 20 is placed in the next top mostleft most position available, using the same rules for polarity. Thisprocess continues in this fashion until all bits placed yielding themessage image 24.

The message image needs to be convolved with the carrier derived fromthe fibrous character of the paper. The process of forming a carrier isdepicted in FIG. 5. Scan area 12 is scanned at a high resolution inblock 26. In a preferred embodiment, the area is scanned at 300 or 600dpi. For concreteness, choose 600 dpi as a preferred scanningresolution. Once this image is obtained, it is transformed to theFourier domain as shown in block 28. The objective of the shaping stepas shown in block 30 is to provide a carrier that maintains the fibrouscharacter of the scan, but also provides an efficient informationcarrying entity. This shaping process is described in detail in U.S.patent application Ser. No. 09/613,989. After the shaping, the image isinverse Fourier transformed in block 31 to form a shaped carrier. Theshaped carrier is rearranged in block 34 as described in U.S. patentapplication Ser. No. 09/613,989. The rearrangement step is intended toprovide an additional level of security. Specifically, because acounterfeiter might determine the region of the paper where the carrieris derived either by the users explicit use of fiducials or by trial anderror, rearrangement of the data in the shaped carrier is a reasonablesecurity measure. The shaped scanned carrier is divided into 16 equalarea regions as also described in U.S. patent application Ser. No.09/613,989. Each of the subregions (64×64) is placed into a differentplace in the carrier image. It is important to make sure that there areno blank areas. To better appreciate this, an illustration is helpful.In this regard, imagine constructing a blank 256×256 image. Next, take aregion from the equally divided area shaped scanned carrier. Place thisin one of the equally divided areas in the blank image. There are 16possible positions. Repeat the process with the next data from theshaped scanned carrier. There are now 15 possible positions to placethis. The rearrangement step allows the carrier data to have 16! (16factorial or 20,922,789,888,000) different renditions. Additionally eachof the carriers can be randomly flipped or rotated (in 90 degreeincrements) to make the counterfeiting even more difficult. Theprescription of the placement steps can be perform in accordance with akey known only to the authentication authorities.

A shortcoming of rearranging the carrier is that it adversely affectsthe robustness of the data-embedding algorithm because during thecarrier formation stage at the authentication step, the regions must berescanned, and any scanning errors introduced, say, in scanning angle,in scanning starting point, or in scanning scale are compoundedproportionately to the number of subdivisions, flips or othermanipulations. These errors affect the algorithms robustness orequivalently the data capacity of the algorithm.

Although the rearrangement step described above can produce a securesystem, another even more secure algorithm can be used eitherindependently or in combination with the above steps. In this regard, asecond carrier is produced with a substantially flat or equivalently,uniform amplitude spectrum, which is also generated from a random key.One method for performing this is described in U.S. Pat. No. 6,044,156by Honsinger, et al. This can be convolved with a first carrier, whichis scanned from the paper either directly or as described above. Theresult of this convolution is a third carrier. The third carrier is usedto convolve with the message. Since second carrier can only bereproduced with the key, the third carrier cannot be reproduced withoutthe key. This provides a system that depends on the media, as in theprior art, and an additional key that is completely independent of themedia itself.

Convolution can be described in either the space domain or the frequencydomain. In the frequency domain, convolution of two functions is thesame as multiplying amplitude spectra and adding the phases. Correlationis identical to convolution in that magnitudes multiply; however, incorrelation phase subtracts. Therefore, convolving an image with auniform carrier preserves the magnitude structure of the image.Correlating with the same uniform carrier will subtract out the phasedispersion induced by the second carrier leaving us with a carriersubstantially the same as in prior art. Since the key is known to no onebut the generating authority and the receiving authority, a very securesystem is available regardless if one subsections and permutes thefibrous region scanned from the media.

Accordingly, the output of the rearrangement step 34 of FIG. 5 isreplaced in the present invention by the output of the process detailedin FIG. 6. FIG. 6. depicts the process of forming a secure dispersedmessage 60. A message image 24 is provided. In a postage application themessage contents can be postage amount, zip codes, or hashes of thedestination address. As described previously, the message can beencrypted, if desired. Next the carrier derived from the media 32 isconvolved with the message image to form the first convolved image.Next, the secret key 56 is used to generate a second carrier 55, whichis convolved with the first convolved image to form the secure dispersedmessage 60. Switching the order of convolution between carrier 28 andcarrier 55 makes no difference to the final output because convolutionsimply adds phase and multiplies the Fourier magnitudes. It isunderstood that convolution can be performed as correlation in theFourier Domain without comprise, as is well known in the art.

As mentioned above, the objective of the shaping step as shown in FIG. 5block 30 is to provide a carrier that maintains the fibrous character ofthe scan, but also to provide an efficient information carrying entity.The shaping step shown in block 30 of FIG. 5 will now be described ingreater detail. The shaping of the amplitude spectrum (derived from theFFT data) is performed with respect to the human visual system andsharpness loss due to the printing process. The human visual system'srole was described during the discussion of FIG. 2 above. Recall thatexcept for near the DC frequency, a Fourier amplitude spectrum iscreated that is proportional the inverse CSF. A carrier derived in thismanner can be improved on further by realizing that when printing animage on a receiver, the modulation transfer function (MTF) of theprinter can be backed out before printing. (A function that expressesthe ability of an optical or electronic device to transfer signalsfaithfully as a function of the spatial of the signal is commonly knownas a modulation transfer function (MTF). The MTF is the ratio of thepercentage modulation of a sinusoidal signal leaving to that enteringthe device over the range of frequencies of interest.)

Therefore except for the very low frequencies around DC, the Fourieramplitude should be proportional to:MTF _(printer) ⁻¹(u,v)CSF _(viewing conditions) ⁻¹(u,v)  (9)(u,v represent spatial frequencies of the two dimensional FFT)

It is important to note that the input data to the FFT is real. Theinput spatial imaginary component is comprised entirely of zeros.However, in the Fourier domain, there will be an imaginary component.After shaping we'd like to make sure that the inverse FFT provides azero valued imaginary component. This ensures that energy defined in theFFT domain was not wasted. The concepts involved with ensuring that theinverse FFT is real is detailed in Honsinger, et al., U.S. Pat. No.6,044,156.

Now, it is well known to those in the practice of image processing thatthe phase contains the important information in an image, maintainingthis information for this application is of paramount importance. Thephase information of the Fourier transform contains the bulk of fibrousstructure information. Only the amplitude spectrum of the FFT datashould be modified during this shaping process. The phase value at eachFourier frequency should always be maintained. Recall that Fourier phaseis given by the equation:θ(u,v)=tan⁻¹(Imaginary(F(u,v))/Real(F(u,v)))  (10)Recall also that Fourier amplitude is given by the equation:amplitude(u,v)=√{square root over(Imaginary(F(u,v))²+Real(F(u,v))²)}{square root over(Imaginary(F(u,v))²+Real(F(u,v))²)}  (11)If one were to multiply both Imaginary(F(u,v)) and Real(F(u,v)) byα(u,v), the phase (see equation 10) is maintained and the amplitudespectrum (see equation 11) is modified. Therefore, the modification ofthe Fourier amplitude spectrum can be performed by multiplying the realand the imaginary components of the Fourier transform by the scalar thatgives us the desired amplitude. If, $\begin{matrix}\begin{matrix}{{\alpha\left( {u,v} \right)} = {{{MTF}_{printer}^{- 1}\left( {u,v} \right)}{{{CSF}_{{viewing}\quad{conditions}}^{- 1}\left( {u,v} \right)}/}}} \\{\sqrt{{{Imaginary}\left( {F\left( {u,v} \right)} \right)}^{2} + {{Real}\left( {F\left( {u,v} \right)} \right)}^{2}}}\end{matrix} & (12)\end{matrix}$Then, the shaping step is simply performed by multiplying each componentof the real and imaginary Fourier coefficients by α(u,v), that is:Imaginary(F _(new)(u,v))=α(u,v)Imaginary(F(u,v))  (13)Real(F _(new)(u,v))=α(u,v)Real(F(u,v))  (14)

When it comes time to extract the message, a user may or may not havethe scanned carrier available. If the carrier is not known beforehand,then it becomes necessary to rescan it from the paper. In this case,assume that the location of the carrier (that is, the location of thefibrous region) is known in advance. The carrier is obtained byrepeating the steps of FIG. 5 with the exception of the rearrangementstep 34. That is, the process of FIG. 5 is terminated at step 32, whichyields the shaped carrier.

FIG. 7 depicts the decoding of the embedded image. The secure embeddedimage 14 is scanned to form the scanned secure embedded image 40. If asecure carrier has not been provided, the steps of FIG. 5 must beperformed on the scan area 12 to form the shaped carrier 32. The shapedcarrier 32 is correlated with the scanned secure embedded image 40.Following this, a key 56 is provided to form the second carrier 55.Optionally, the second carrier 55 may be stored instead of the key. Theresult of the correlation between the shaped carrier 32 and the scannedsecure embedded image 40 is correlated with the second carrier 55. Theresult of the second correlation is the extracted message image 65. Theextracted message can now be decoded using the art described above. Asmentioned above, one needs to know where the bit values of the extractedmessage image 65 are located to properly interpret the message contents.

Referring now to FIG. 8., the result of finding the location of each biton the extracted message image 65 and tabulating the bits in apredetermined way is the extracted encrypted message 70. The extractedencrypted message 70 is decrypted 72 using a private key. The result ofthis is the embedded message 74. The embedded message is interpreted 78by comparing to a table stored in the computer or computerized device.The table delineates all of the known valid messages. If the embeddedmessage is the same as a known valid entry, then the letter is declaredauthentic, if not, the letter is declared suspicious or invalid and isgiven special attention.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

Parts List

-   2 binary message image-   4 iconic message image-   12 scan area-   14 secure embedded image-   16 message-   18 encryption-   20 bits from encryption-   22 message template-   24 message image-   26 scanning-   28 transforming-   30 shaping-   31 inverse transforming-   32 media-   34 rearrange-   40 secure embedded image-   55 second carrier-   56 secret key-   60 dispersed image-   65 extracted message image-   70 extracted encrypted message-   72 decrypted-   74 embedded image-   78 message interpreter

1. A method for creating an authenticable image on a receiver, themethod comprising the steps of: (a) providing a first carrier formedfrom information related to a physical characteristic of the receiver;(b) providing a second carrier that is randomly generated; (c) combiningthe first and second carrier such that the first carrier cannot bederived without the second carrier for forming a combined carrier; (d)combining the combined carrier with predetermined content for formingthe authenticable image having the predetermined content; and (e)including the authenticable image having the predetermined content onthe receiver.
 2. The method of claim 1, wherein step (a) includesproviding fibrous content as the discernible physical characteristic ofthe receiver.
 3. The method as in claim 2, wherein step (a) includescreating the first carrier from scanning a predetermined region of thereceiver.
 4. The method of claim 1, wherein steps (a) and (b) includecreating the first and second carriers by: i) transforming the carrierto a Frequency domain to form a transformed carrier; ii) shaping aspectrum of the transformed earner to cancel the anticipated MTF effectof the print process or to facilitate the human visual system; and iii)inverse transforming the transformed carrier.
 5. The method of claim 1further comprising the step of encrypting the predetermined content. 6.A method of authenticating a receiver having an authenticable image thatincludes predetermined content integrally combined with informationrelated to the discernible physical characteristic of the receiver, andintegrally combined with a second carrier generated from a random key,the method comprising the steps of: (a) scanning the authenticatableimage on the receiver to produce information related to the discreniblephysical characteristic of the receiver; (b) discerning the physicalcharacteristics to form the first earner; (c) providing a second carriergenerated from a random key; (d) discerning a message using the firstand second carriers in combination with the scanned authenticable image;(e) providing the predetermined content; and (f) determining theauthenticiy of the receiver upon comparing the message with thepredetermined content.
 7. The method of claim 6, wherein step (c)includes discerning the physical characteristic of the authenticatedreceiver by scanning a portion of the receiver on which theauthenticatable image is formed.
 8. The method of claim 7, wherein step(c) includes determining fibrous content as the discernible physicalcharacteristic of the receiver.